It is common practice in the building of tires to fold the edges of unvulcanized, rubberized ply material around, for example, bead wire bundles by the use of inflatable bladders located on the tire building drum. In use they are inflated and moved or rolled axially of the drum either by means of an axially movable cage, a curved surface known as a can, or a second inflatable bladder.
While it is relatively simple to fold a ply around a rigid member such as a circumferential wire bead bundle by means of a bladder, the matter becomes complicated where a ply is to be folded upon itself or around the edge of another ply. In the latter situation, since no back-up material is present against which the ply may be folded, the best previously known method for initiating and folding a ply along a true circumferential line has been the manual method.
This time-consuming process involves the use of two hands, limiting the work area to one edge at a time; it also creates localized and irregular material-distortion, resulting in uneven folds, wrinkles and trapped air.
The object of the present invention is to provide apparatus for initiating and forming sharp, uniform circumferential folds in tire ply material which is turned upon itself or around the edges of other ply material, without the need for pre-creasing or separate pusher elements. Of particular benefit in building tire-belt units comprising rubberized cord-material, there is provided, according to the invention, an annular inflatable bladder anchored circumferentially on a building drum and provided with certain external, shaped members which aid in folding the fabric ply uniformly and wrinkle-free along a true circumferential line.
An example of the construction in which ply material is folded about a rigid member is seen in U.S. Pat. No. 3,111,443 to Vanzo et al, wherein bladder chambers at the shoulders of the tire building drum are inflated and caused to fold ply material around a wire-bead by the axial motion of a tubular pusher-can or -bell. There is no teaching of a fabric-folding without the back-up or anchorage of a rigid bead-member, nor use of a bladder without an axial pusher-means.
In U.S. Pat. No. 3,560,301 to Cantarutti there is shown similar ply-folding, but only around a rigid bead-member, as well as a pushing of the bladder axially, in this instance by a second inflatable bladder.
Attempts have been made to anchor the ply material out to the intended fold-line, without a rigid bead, such as by the application of a vacuum, shown in U.S. Pat. No. 3,154,455 to Nebout, but the folding action is again caused by an axially moving rigid sleeve.
Another method of anchoring the ply material is shown in U.S. Pat. No. 3,966,536, to Schmitt, wherein the material is first adhesively secured to its underlying support body, out to the intended fold-line. However, the crease in the material is actually started by moving a profiled stitcher-roller along the underlying support body and against the edge of the cylindrical bell.
U.S. Pat. No. 4,087,306 to Head et al discloses a turn-up bladder having an uninterrupted cylindrical wall and varying zones of body construction, but without the lifting and turning members of the present invention.